ECG rhythms Sinus rhythms
Sinus tachycardia ECG
Sinus tachycardia. Regular, above 100/min, with an upright P wave and a normal PR before every narrow QRS.
A 30-second recording of the heart model, played in real time. Run live starts the engine itself with this rhythm.
Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.
Measured on this recording
| Ventricular rate | 115/min |
|---|---|
| PR | 145 ms |
| QRS | 84 ms |
| QT | 303 ms |
| QTc (Bazett) | 422 ms |
| QTc (Fridericia) | 378 ms |
What it is
A sinus rhythm faster than 100/min. The sinus node fires faster, usually as a normal response to a demand on the body; the P wave and PR stay normal and every P wave conducts.
How to read this strip
| Rate | Above 100/min. |
|---|---|
| Rhythm | Regular. |
| P waves | Upright in II, one before every QRS. |
| PR | Normal and constant. |
| QRS | Narrow. |
| QT | Normal for the rate. |
Causes
- Fever, infection and sepsis.
- Pain, anxiety, exercise.
- Hypovolemia: bleeding, dehydration.
- Hypoxia, pulmonary embolism, heart failure.
- Anemia, hyperthyroidism, hypoglycemia.
- Shock or hypotension of any cause.
- Drugs and withdrawal: caffeine, cocaine, amphetamines, anticholinergics, beta-agonists; alcohol or beta-blocker withdrawal.
What to consider
- Treat the cause, not the rate: slowing a compensatory tachycardia can be harmful.
- Onset and offset are gradual and the rate varies with activity and breathing; an abrupt start and stop points to a re-entry tachycardia.
- A rate fixed near 150/min that does not vary should prompt a search for atrial flutter with 2:1 conduction.
- Persistent sinus tachycardia without an obvious cause deserves evaluation (for example pulmonary embolism, thyroid disease, anemia); inappropriate sinus tachycardia and postural orthostatic tachycardia syndrome (POTS) are diagnoses of exclusion.
Key point
Sinus tachycardia is a sign: look for fever, pain, low volume, hypoxia, anemia or sepsis before treating the rate.
Not to be confused with
- Paroxysmal supraventricular tachycardia (re-entry) — Re-entry SVT usually shows no clear P wave before the QRS. Here a normal P wave precedes every beat.
- Atrial flutter with 2:1 conduction (simulator) — Flutter at 2:1 also runs near 150/min, but there is no evidence of a second atrial wave between the complexes; one normal P wave sits before each QRS.
- Atrial fibrillation — The rhythm is regular and P waves are clearly present.